Growth hormone stimulates the collagen synthesis in human tendon and skeletal muscle without affecting myofibrillar protein synthesis.
Level 2 - randomized trial
Randomized controlled trial evaluating the effects of short-term recombinant growth hormone administration in humans.
PubMed 19933753 · doi:10.1113/jphysiol.2009.179325
What was done
Healthy young individuals were administered recombinant human growth hormone (rhGH) at 33–50 µg·kg⁻¹·day⁻¹ for 14 days. Researchers measured circulating GH and IGF-I, local tissue IGF-I mRNA, collagen I mRNA expression, collagen protein synthesis, and myofibrillar protein synthesis in both tendon and skeletal muscle, as well as the interaction with moderate exercise.
What was found
Administration of rhGH elevated serum GH, serum IGF-I, and tendon and muscle IGF-I mRNA expression. Tendon collagen I mRNA expression increased 3.9-fold (P < 0.01) and tendon collagen protein synthesis increased 1.3-fold (P = 0.02). Muscle collagen I mRNA expression increased 2.3-fold (P < 0.01) and muscle collagen protein synthesis increased 5.8-fold (P = 0.06). Elevation of GH and IGF-I did not affect myofibrillar protein synthesis, and moderate exercise did not enhance these effects.
Why it matters
The findings indicate that growth hormone stimulates connective tissue matrix synthesis rather than contractile myofibrillar hypertrophy, explaining its role in tendon and matrix adaptation rather than direct muscle fiber building.
Limits
The abstract does not disclose the sample size, control group details, or sex breakdown. The intervention lasted only 14 days, muscle collagen protein synthesis changes were marginally significant (P = 0.06), and clinical outcomes such as tissue tensile strength or injury recovery were not measured.
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